In a radio communication system, a radio terminal apparatus connects to a radio base station and performs data communication via the radio base station. Such a radio communication system is widely used today. The timing when the radio terminal apparatus performs data communication is dependent on a user operation. Therefore, there may be a period during which data communication between the radio terminal apparatus and the base station is intensive, and a period during which there is no data communication. For example, when the user accesses to a Web site, data of the Web page is received in bursts. Then, while the user is browsing the Web page, no data is received.
It is costly and inefficient for a radio communication system to have data communication between a radio terminal apparatus and a radio base station available at any time even during the period in which there is no data communication. In view of this, some radio communication systems are designed such that, if there is no data communication for a certain period of time, a radio terminal apparatus may periodically and discontinuously perform transmission and reception.
For instance, discontinuous communication control called Continuous Packet Connectivity (CPC) is defined by High Speed Packet Access (HSPA), which is a communication standard developed as an extension of Wideband Code Division Multiple Access (W-CDMA).
According to CPC defined by HSPA, a radio network controller (RNC) in a radio access network notifies a radio terminal apparatus of a discontinuous reception (DRX) period and a discontinuous transmission (DTX) period.
The radio terminal apparatus discontinuously receives control information on a downlink control channel from a radio base station in the notified DRX period. When there is data to be transmitted in the downlink, the presence of data is notified to the radio terminal apparatus at the next DRX timing. Further, the radio terminal apparatus discontinuously transmits control information on an uplink control channel to the radio base station in the notified DTX period. When there is data to be transmitted in the uplink, the presence of data is notified to the radio base station at the next DTX timing.
With regard to control of discontinuous communication, a mobile communication system has been proposed that includes a radio base station and a plurality of mobile stations which are operable in three modes: active mode, idle mode, and battery saving mode (see, for example, Japanese Laid-open Patent Publication No. 2005-26991). This radio base station sets the transmission period of a paging channel to 40 ms if the mobile station is operating in the idle mode, and sets the transmission period of the paging channel to 80 ms if the mobile station is operating in the battery saving mode. Thus, the mobile station receives the paging channel in the period set by the radio base station.
In the mobile communication system described above, a common reception period of 40 ms is set for all the mobile stations that are operating in the idle mode, and a common reception period of 80 ms is set for all the mobile stations that are operating in the battery saving mode.
However, it is difficult to determine a reasonable fixed communication period for all the radio terminal apparatuses. If the communication period increases, the time period during which a transmission circuit and a reception circuit of the radio terminal apparatus may be suspended increases. Therefore, it is possible to reduce power consumption of the radio terminal apparatus.
However, an increase in the communication period might increase the time lag between when data communication is requested in response to a user operation and when data communication actually starts. This results in a delayed response to the user operation. Accordingly, the communication period appropriate for a radio terminal apparatus varies depending on the tendency of user operations.